WASHINGTON Nevada Republican John Ensign, who admitted having an extramarital affair with a campaign staff member, said on Thursday that he would resign from the Senate on May 3.
Ensign, 52, announced last month that he would not seek re-election in 2012. He had been facing a Senate ethics committee probe stemming from the extramarital affair.
"While I stand behind my firm belief that I have not violated any law, rule, or standard of conduct of the Senate, and I have fought to prove this publicly, I will not continue to subject my family, my constituents or the Senate to any further rounds of investigation, depositions, drawn out proceedings or especially public hearings," Ensign said.
"For my family and me, this continued personal cost is simply too great," the senator said in a statement.
Ensign will submit a letter of resignation to Vice President Joe Biden, who is also president of the Senate, on Friday, the statement said.
Nevada's Republican Governor Brian Sandoval will appoint a temporary replacement, expected to be another Republican, to fill the remaining 20 months of Ensign's term so there would be no change in the balance of power in the Senate.
Democrats now control the Senate, 53-47.
Ensign admitted to having an affair in 2008 with Cynthia Hampton, who worked for his campaign, and whose husband, Douglas, was a legislative aide to the senator.
The Senate ethics investigation focused in part on some $96,000 Ensign's parents gave to the Hamptons, which Ensign's attorney has characterized as a gift.
The heads of the Senate Ethics panel said in a joint statement that Ensign "has made the appropriate decision."
Douglas Hampton was indicted late last month on suspicion of trying to lobby and seek assistance from his former boss on behalf of his new employers, an airline and an energy company.
Ensign is the third Senate Republican to decide not to seek reelection, following Assistant Senate Republican Leader Jon Kyl of Arizona and Kay Bailey Hutchison of Texas.
Five Senate Democrats have said they won't seek another term next year: Democrats Daniel Akaka of Hawaii, Jim Webb of Virginia, Kent Conrad of North Dakota, Jeff Bingaman of New Mexico and independent Joe Lieberman of Connecticut.
Two Nevada representatives, Democrat Shelley Berkley and Republican Dean Heller, were already vying for Ensign's seat.
Jennifer Duffy, who tracks Senate races for the nonpartisan Cook Political Report, said the resignation could mean an advantage for the Republican in what is expected to be a hotly contested race in 2012.
"Republicans stand to benefit assuming the Republican governor appoints Heller, which affords him the benefits of incumbency and boosts his fundraising," Duffy said. "That said, I still believe the race is a toss up."
(Reporting by JoAnne Allen and Thomas Ferraro; editing by Anthony Boadle)